WASHINGTON — The Syrian opposition's record so far in handling tens of millions of dollars in U.S. humanitarian and other nonlethal assistance paints a bewildering picture of logistical challenges ahead of any delivery of American weapons and ammunition.

No aid shipments appear to be heading to terrorists or corrupt hoarders, according to U.S. officials, but packages of food, medicine and other lifesaving supplies regularly face long delays because of political rivalries among various rebel factions.

Anecdotes abound.

An American shipment of humanitarian goods was held up for two weeks amid a dispute between opposition groups over whose label should be attached to the boxes, a senior administration official recounted this week. Aid-filled planes have landed in neighboring countries with no trucks at the landing sites for transporting the items into Syria. In Cairo, funds the U.S. was prepared to provide an opposition political office were flat-out rejected, the official said, speaking on condition of anonymity because the official wasn't authorized to discuss the issue publicly.

Although the Syrian opposition's described dysfunction is nothing new, its problems are getting increased scrutiny since the Obama administration's decision last week to authorize for the first time lethal military support to units fighting to overthrow President Bashar Assad's regime.

Secretary of State John Kerry plans to use a meeting Saturday in Doha, Qatar, of officials from countries allying themselves with the rebels to underscore the need for coordinating and funneling aid through the Supreme Military Council, senior State Department officials said Friday. The U.S.-favored group is overseen by Gen. Salim Idris, a defector from Assad's military.

The aides, speaking on condition of anonymity because they were not authorized to talk publicly about Kerry's trip, said Kerry also hopes the meeting will re-energize a newly expanded group of Syrian opposition leaders that is scheduled to elect new leadership in coming days.

Beyond that, the Obama administration's plans are unclear. Kerry held two classified briefings with members of Congress on Thursday. No details emerged about what types of weapons could be sent, where and when they'd be delivered or who exactly would be the recipients. The lack of clarity rankles both lawmakers who want more forceful U.S. action as well as those who say the U.S. should stay as far away as possible from Syria's brutal two-year civil war.

"All I know is what I've read in the media and that is light weapons," said Sen. John McCain, R-Ariz., a leading proponent of taking a bigger military role in Syria. "That's clearly not only insufficient, it's insulting. We've got to take out their air assets."

Sen. Lindsey Graham, R-S.C., another supporter of arming the rebels and other steps such as establishing a no-fly zone over Syria, said he also had no understanding from the Obama administration about what form future lethal aid might take and possible delivery dates.

Sen. Bob Corker, R-Tenn., was even more critical. ""We have the ability right now to fully understand who is the type of individual or group that meet our standards, and I think we've had that information and ability for probably nine months," he said. "Will there be mistakes made? Of course, but I do think it helps to put our thumb on the scale."

Meanwhile, Senate opponents of arming the rebels moved Thursday to block Obama from providing any military support at all. The bipartisan group including Sens. Tom Udall, D-N.M., Mike Lee, R-Utah, Chris Murphy, D-Conn., and Rand Paul, R-Ky., introduced a measure to prohibit the president from using any money to increase U.S. involvement in the conflict. Specifically, it would ban the Pentagon, CIA and other intelligence agencies from funding military, paramilitary or covert operations in Syria.

"We need to place a check on the president's unilateral decision to arm the rebels, while still preserving humanitarian aid and assistance to the Syrian people," Udall said.

Paul said the president's decision was "incredibly disturbing, considering what little we know about whom we are arming. Engaging in yet another conflict in the Middle East with no vote or congressional oversight compounds the severity of this situation."

Neither Obama nor any other member of his administration has publicly confirmed that the U.S. has authorized lethal aid for the rebels, though since last week several officials have acknowledged as much on condition of anonymity. The closest anyone came was Ben Rhodes, Obama's deputy national security adviser. He said last week that U.S. confirmation of chemical weapons use by the Assad regime has prompted American support to the Syrian rebels of increased "scope and scale."

Obama himself refused to provide any specifics when asked at a news conference this week in Germany.

The U.S. is most likely to provide rebel fighters with small arms, ammunition, assault rifles and a variety of anti-tank weaponry such as shoulder-fired rocket-propelled grenades and other missiles, according to officials. They haven't disclosed which specific weapons have been approved or when and how they might be delivered. The officials, who've demanded anonymity because they weren't authorized to speak publicly about the matter, said any weapons and ammunitions are unlikely to make it to vetted Syrian rebel units before August.

The opposition's track record in handling aid has been discouraging.

U.S. officials said almost all of a $127 million package of ready-to-eat meals, medical kits and other nonlethal assistance announced earlier this year has been delivered to Syria. U.S.-provided food has made it from Turkey to as far south as Hama and Homs, and to the southeast border with Iraq. Humanitarian assistance reaching the besieged city of Qusair, which Assad's forces conquered from the rebels earlier this month, was limited pretty much to medical supplies.

The senior administration official said the U.S. is monitoring for aid being diverted, but so far hasn't found any instances of it. That could provide Obama with some confidence in the Syrian opposition's ability to ensure that U.S.-supplied weapons and ammunition don't fall into the hands of al-Qaida-linked extremists. The fear that it might has long been one of the administration's primary explanations for why the U.S. wouldn't arm the anti-Assad rebellion.

Syria's opposition, however, remains problematical. Because of constant bickering among its various branches in Turkey, Egypt and inside Syria, U.S. officials say they have often been forced to act as go-betweens, if only to get the opposition to sign off on some of the aid it originally requested.

Some $5 million in U.S. aid has gone to helping the opposition establish an office in the southern Turkish city of Gaziantep and expand its staff from a handful of employees to a staff now of about 100, including many in liberated parts of Syria. In Aleppo, American-trained search and rescue personnel have helped dig survivors out of buildings struck by Scud missiles. The U.S. is also training policemen and providing them uniforms in an effort to build the opposition's credibility with the Syrian population.

Those are the successes.

On the other hand, disputes between local authorities and the opposition leaders outside the country has held up elections in parts of Syria wrested from Assad's control. The two sides have been unwilling at times to even talk to one another, the senior administration official said. When the U.S. offered to provide hospitals with emergency generators, a fight erupted over which cities and which politician's preferred recipients should get priority. The result was shipping none of them until the generators could go simultaneously to all the hospitals on an opposition list.

When the U.S. offered to provide the opposition headquarters in Cairo some $2 million to buy phones and computers and hire staff, Syrian opposition leader Moaz al-Khatib rejected the aid, citing administrative costs that the U.S. also was picking up, the official said.

One thing any future aid package will include is trucks. With Obama ruling out any American military boots on the ground in Syria, it is up to the opposition itself to transport goods received in Turkey or Jordan to civilians in Syrian cities or fighters on the battlefield. And so far it has struggled on this account, according to officials.

State Department spokeswoman Jen Psaki said Thursday that the next package of nonlethal U.S. assistance would include at least $16.6 million in "combat support assistance," which includes trucks, communications gear and medicine. Other funds will go to reconstruction efforts, university scholarships, activist training and democracy-building efforts.